The present invention relates to a method of and an apparatus for controlling an electronically controlled transmission for use in an automobile.
Vehicles, typically automobiles, powered by internal combustion engines have a transmission coupled between the engine and driven wheels for effective utilization of output power from the engine. In operation, one of several different gear ratios of the transmission is selected to meet the particular vehicle speed. For example, when the vehicle is to run at a low speed, a larger gear ratio is used.
A transmission system having a hydraulic drive mechanism controlled by a computerized electronic control unit for automatically driving an internal lever which selects transmission gears has been put into use recently. The transmission system has a select actuator for driving the interval lever selectively in a Y direction, and a shift actuator for driving the internal lever in an X direction perpendicular to the Y direction. The computerized electronic control unit has a memory for storing data known as a shift map, representing transmission gears corresponding to automobile speeds and degrees of depression of an accelerator pedal. While the automobile is being driven, the electronic control unit detects the depression of the accelerator pedal at all times and searches the shift map based on the detected pedal depression data for determining an optimum transmission gear. Then, the electronic control unit issues a command to operate the shift and select actuators alternately to select an optimum transmission gear ratio.
The electronic control unit for the electronically controlled transmission operates as follows: While the automobile is running on a flat road at a speed of 50 Km/h with the accelerator pedal depressed 20% of its full stroke, the optimum transmission gear is the top gear (3rd forward-gear position, for example). As the automobile starts running up a steep upgrade, the speed of the automobile drops rapidly. To avoid the speed drop, the driver responds by depressing the accelerator pedal successively by 20%, 30%, 40%, and finally more than 80% of its full stroke. At this time the accelerator pedal moves through a range of 40% of the full depression stroke requiring a gear change from the 3rd to the 2nd gear. The electronic control unit detects the depression of the accelerator pedal and issues a command to the shift and select actuators to shift the transmission from the 3rd gear to the 2nd gear. If, after the transmission has been shifted, the accelerator pedal is still depressed by more than 80% of the full stroke, the electronic control unit detects this depression of the accelerator pedal and issues a command to the shift and select actuators to shift the transmission from the 2nd to the 1st gear. Due to the gear change from the 3rd to the 2nd gear, the speed of the automobile is reduced gradually. Therefore, upon completion of the gear shifting operation, the speed of the automobile has already been reduced to a large extent. The conventional electronic control unit is, consequently, disadvantageous in that the transmission is shifted stepwise from the 3rd to the 2nd to the 1st gear while the shifting operation is being carried out, and any following automobile operation is delayed.